1. Field of the Invention
The invention relates to electrochemical sensors, and in particular to a sensor for measuring electrochemical activity of a selected species in a flowing material.
2. Description of the Prior Art
A wide variety of electrochemical sensors have been developed and used for industrial applications. For example, pH sensors have been used for many years and commonly make use of an indicator electrode and a reference electrode. The indicator electrode is commonly a pH sensitive glass member which contains a suitable electrolyte and in which is immersed an internal reference. The reference electrode commonly contains a reference solution (an electrolyte) and an internal reference. Unlike the indicator electrode, the reference electrode also includes some form of junction for establishing contact between its internal electrolyte and the liquid being tested. The sensor output signal is in the form of a potential between the indicator electrode and the reference electrode.
When this type of sensor is used to measure electrochemical activity in a flowing liquid, there are a number of potential sources of inaccuracies and problems which are encountered. In particular, streaming potentials caused by the flow of fluid past the indicator electrode and reference junction and stray electric current can both result in inaccurate potentials being produced. Sensors of this type have generally been rather fragile, and the insertion of the sensor through a sometimes obstructed passage into the fluid, and the possible presence of stream debris, can result in cracking or breaking of the indicator electrode. Fouling of the sensor by debris contained in the liquid stream also presents a problem with prior art electrodes.